One Punch Man Gaiden - Birth of Genos
by Idyllicdream
Summary: There are questions about Genos' past that was never answered. What happened to him four years ago? How did he become a cyborg?On his road to recovery, with the help of he doctor who saved him and a mystery apprentice, Genos learns through his own struggle. But in his quest to become strong, will Genos abandon his own humanity? Or, before all is over, will he discover his own path?
1. Chapter 1: Metal Heart

1

Metal Heart

* * *

There was one thing Genos would never forget in his life.

Pain.

The crushing weight on him was beyond what he thought possible. Then again, he was very young and very naive. A meek 15 year-old boy, who didn't know much of just how painful the world can be.

That day reminded him. And it also changed him.

It's a cruel world out there, and pain was all to be felt.

But right now the pain was all-consuming. Especially...the pain that came from his limbs. His arms, his right leg, and the left side of his chest. There was the despair that was devouring him. His heart had ached with so much grief he had forgotten almost what he was grieving for.

Pain.

There was such an abundance of it that Genos simply couldn't tell which came from his body or which came from his mind.

Whatever was left of both.

There were moments when the pain became overwhelming, the boy felt like bursting into tears of anguish. But he didn't. So in the deep reaches of his mind which hadn't been clouded by some sort of hurt, he wondered if he had lost the ability.

...Then again, maybe he wasn't just human anymore.

Humans cry. He heard even some animals cry when they are suffering.

But he didn't. And Genos wondered if he would be able to anymore.

After all, he was becoming a cyborg. Half-machine. It would only make sense that he also gave up his humanity to exact his revenge.

* * *

"-kun...Genos-kun." He heard a soft voice calling him.

"...Doctor?"

He was surprised he could use his voice. It sounded like a stranger's voice, like an echo. Genos tried to open his eyes, blinking a few times. It was a miracle, when the colours started flooding in his vision, and kind sounds filled his ears.

Dr. Stench breathed a sigh of relief. He seemed to turn his head around and whisper something with a smile to someone beside him, but Genos wasn't sure. He squinted his eyes, hoping to catch a clearer glimpse of his saviour. Yet his eyes were still hazy. That was to be expected.

"-signs are stable. He'll be alright."

His hearing seemed to be better. He recognised the doctor's voice. This was quite ironic, because when Dr. Stench found him in the rubbles - saved him, Genos had such difficulty discerning his voice. Dazed and disoriented aside, there'd been a buzzing, uncomfortable ringing in his ears, which he just couldn't seem to shake off!

It was later that Genos realised he had been deafened by the explosion which had destroyed his hometown. Not only was he mortally injured, he'd also lost his hearing and almost all of his sight. Though Genos barely survived, he would have died soon afterwards had it not been for a passing scientist. And he would have never recovered the ability to see or hear, had it not been for this man.

Dr. Stench suddenly exited Genos' limited field of vision. A small part of him panicked. What at? At being abandoned? At reliving the experience of nearly dying? There were too many answers.

But then another face came into his line of sight - blurry as it was, it was getting clearer. His surprise momentarily calmed him down.

Despite the dreadful situation he was curious to see who it was.

It was the face of a girl. Who had very soothing features. Dark hair framed her face and was parted to the side as she leaned in to see him. Like the doctor, she had a gentle presence. She seemed younger than him. But her eyes weren't. They were kind, and a brightness lingered in them. But the light radiated from a depth which reminded him of the emptiness he felt. Of what he experienced.

That was how he knew she had gone through something just as horrible.

"Nanako, leave Genos alone. The boy needs his rest." The Doctor's voice rippled through them.

"Yes, Doctor."

The girl's face moved further away from him, although he still watched her. It appeared that her eyes, also, lingered on him. He wondered, did she pity him?

Genos finally looked away. He began to wonder why he was surprised to see someone else. Dr. Stench was clearly talking to another person in the room, he analysed. How many were there? Just him and Nanako? Or were there others?

"When I told Nanako to move away, I do expect you to get some rest, Genos-kun." Dr. Stench came next to him, smiling. "You have fought well. And you will fight well. But now, have nothing to fear. It is just you and I and Nanako. Sleep."

His words washed over Genos like a calming wave. Somehow, being next to him and hearing him speak, Genos' fears dissipated like shadows. He allowed himself to feel the wounds on his soul. The scars would not disappear so easily, but for not the trauma subsided. Slowly, he closed his eyes.

His last thoughts before restful sleep claimed him, was that he no longer felt pain.

.

.

* * *

A/N:

I recently discovered this awesome called One Punch Man and L.O.V.E.D it! The humor, the drawing style, the non-cliches! It was epic!

Genos' past was a great curiosity for me though. Questions like where he came from, who is the mysterious cyborg and who Genos was before he became...well, Genos bothered me for a while. And I thought there were so many intriguing things, so many potential answers yet to be explored! That was where this story came from, my own guess into Genos' past. I looked up information so this story can be as canon as headcanon can be XD

Have fun reading. Please review!


	2. Chapter 2: Dr Stench's forboding

Chapter 2

Dr. Stench's forboding

 _"Doctor, the transforming process is not going well. His body is rejecting the prosthetic parts."_

 _The sound of a person's voice injected deep into Genos' consciousness. He could hear it clearly, even the worry, yet his eyes remained closed. His body did not move. It was as if he was still asleep, awake and dreaming._

 _"What's going to happen to him?" The voice continued, no less anxious than before. He wondered who on earth would sound so concerned about his wellbeing._

 _"Be calm, Nanako. Genos-kun will be fine. I won't let him die."_

 _Ah, this voice. It's Dr. Stench's. It carried the wisdom and weariness of many years. It was perhaps the only voice Genos could recognise without much trouble. It was undoubtedly the voice of his saviour._

 _Nanako, even though he couldn't see her face, was clearly very worked up about something. He could almost picture her frown in his mind. "Doctor, you shouldn't have agreed to his request in the first place. Do you really think anyone who survived hell would think straight? It's already enough that you saved his life."_

 _Dr. Stench, on the contrary, was rather patient-sounding. "Nanako, you know I owe him much more than that. It is my fault, after all, that he has no family to go back to."_

 _His voice strained uttering that last part. Genos could imagine his face was buried in his wrinkled hands, old features worn as if bearing the burden of many deaths. Genos himself suddenly exhaled sharply, smothered by weight on his chest._

 _"So you think it's right to condemn him to living for revenge?" Nanako continued, voice equally forced. "I don't understand you, Doctor."_

 _"No, you won't. You're too soft at heart."_

 _The doctor sighed, saying compassionately. "People need a reason to live. I believe the boy's found a purpose to keep him going. If he didn't, I doubt there's anything I can do to carry him back from the brink. You, of all people understand this, right?_

 _"Everything that is done in the world is done by hope. So it goes with courage."_

 _There was a sullen silence. Displeased, but nonetheless no longer so tense. Dr. Stench seemed to have an effect on her. After a moment, there were footsteps and Nanako's voice sounded distant._

 _"I hope you don't end up killing him, Doctor."_

 _She closed the door behind her. Though she took care to close it carefully, it still resonated in Genos' mind._

.

* * *

.

"You're awake, Genos-kun."

Dr. Stench sounded delighted, as if he had been expecting him to come to. The man's face was layered with concern and kindness as he strode over to Genos' side. The boy wondered how the doctor knew he had regained consciousness, because his eyes had only blinked a few times before he heard Dr. Stench call his name. There must be a life monitor somewhere, with electrodes plastered to his temples.

"Doctor." Genos said simply.

The scientist made a quick scan of the many computer screens that surrounded Genos and his room. Which, he noted, was rather looking like a lab than one fitted for a human.

Yes, this is perhaps more cut out for his current needs, Genos thought, slightly embittered. A machine like him should have no need for comforts.

"This is good news," Dr. Stench's pleasing tone turned Genos' focus away from the dour architectural design. "Your readings seem much more stable than before. Would you like to sit up?"

"That would be very welcomed, sir." He replied.

As Dr. Stench adjusted the bed's inclination, Genos took time to take note of other things in his immediate surrounding. For one, he and Dr. Stench were alone, save for the glinting of several fibre-optic instruments. The girl he had seen last he woke was nowhere to be found. He also discovered that there, in fact, were no electrodes stuck to his head like he had expected, which somewhat baffled him.

Genos found himself taking in stride everything in an unperturbed manner, as if he'd been here before and nothing could faze him. With nothing else to think about, he once again re-focused on Dr. Stench, who was surveying a small clipboard. His saviour chuckled and put the board aside and smiled serenely at Genos.

"Genos, if you don't mind, there are a series of tasks I'd like you to try. They will be very simple, nothing strenuous. But it shall put my mind at ease that you're taking everything well."

"Yes, Doctor. I don't mind." Genos accepted without so much as questioning him.

 _Such a dutiful boy_ , Dr. Stench thought to himself with a tinge of sadness. He then carefully instructed Genos on his tasks, which ranged from simply stretching his fingers and moving them, to picking up light objects like a pen. When Genos proved he could manage the latter quite well, Dr. Stench asked him to write something down on a note.

Some tasks soon get tedious, but all the while the doctor kept his voice patient and cheerful. Genos also didn't make any complaints whatsoever for the whole duration.

He then asked questions like whether the boy was hungry, feeling cold or cramped, to which he methodically replied. This raised Dr. Stench's concern a bit, because the boy appeared to have an apathetic lack of reaction to anything that might discomfort him.

 _The boy had just had a traumatic experience, let him heal._ Stench thought to himself. But his worries weren't easily chased. For apathy, more than any rile emotion, was dangerous. It could turn a modest man into being capable of extraordinary cruelty.

The wise doctor then concluded that he must be watchful the boy. His physical recovery will mean nothing if his soul is not saved.

"That will be all for today," He told Genos, smiling jokingly. "Did you find that awfully boring?"

"Not really, Doctor. I understand its necessity." Genos replied and breathed in meditatively.

"I see. An understanding patient makes a doctor's life surprisingly easier." Dr. Stench nodded sagely. "For the rest of the day I'd like you to rest and recoup as much as possible. If you need anything, just press that button and someone will come for you."

Genos gave the button a contemplative stare. He couldn't think of any use he could have for it. His present state was so detached from worldly needs that he could frankly enter nirvana.

No, he probably couldn't. Because against the stage of his outer calmness and composure was a backdrop of smouldering anger like live coal - a rage that could not be quenched by any meditation or rest. It was sizzling and growing by the day, by the waking hour and fuelled by a desire to get out, get stronger and achieve his one desire.

Revenge.

No one as tainted with hate as he could find peace in nirvana.

Perhaps Dr. Stench could sense the change, the monster within Genos. Even if he hadn't known the boy personally. All the more, he became concerned.

He sighed and his hand landed softly on Genos' head. "Rest that turbulent mind of yours for now, Genos. For now, feel nothing but that you are alive and recovering."

He ruffled Genos' hair. And the boy was silent. He felt guilty at troubling his saviour with his mental state, but at the same time, he only wanted to grieve. And the only way he could grieve now was to nurture his anger. After all, his home had been blown to bits. There was not even a grave from which he could mourn his dead parents and older brother.

.

* * *

.

"Nanako, do you think I've done the right thing?"

The girl was startled by the degree of vulnerability in her doctor's voice. The man sat still in his chair, his elbows resting on his knees, his eyes closed. His features were as solemn and ancient as old trees in the forest. She had rarely seen him so troubled and fearful before.

"I'm not sure, Doctor. I stand by what I said to you before, that I doubt anything good could come from letting a person live solely for revenge." She said evenly, eyeing him with sympathy for his weariness. He had tended to the cyborg boy for many days as to exhaust him. "So it's your turn to stand by what you said, Doctor. Have faith in him."

A silence full of understanding slowly permeated through them both. The young girl could feel the anxiety in her mentor lessoned, and she smiled and secretly thanked the powers that be. It worried her a great deal to see her doctor's resolve shaken, but she was glad and relieved now that he was no longer doubting.

"Thank you, Nanako. You're a saint, you know that?" Dr. Stench leaned back in his chair, his face alight. The solemn lines had vanished, leaving a natural tranquility that Nanako loved.

She laughed quietly. "You make it too easy, Doctor."

The grey-haired scientist sat in his old chair pensively, watching Nanako as she cooked and stirred some Yakisoba and hummed some old tune. As the soba, beef and vegetable hissed on the pan, the doctor suddenly said.

"I still feel the need to be concerned, Nanako. It' been a month since the incident, and Genos either feels too much or too little."

"Oh, Doctor. I'm sure it's nothing to do with his teenage years." Nanako lightly replied, but Dr. Stench knew behind the good-humored tone Nanako was very serious.

"You're a teenager, too." He teased.

Nanako spun around, a large wooden spoon still in hand and she brandished it like a deadly weapon. "I'll have you know that I'm _nothing_ like those hard-headed teenage boys." She said sullenly. Her mentor laughed and, although not entirely content, Nanako turned back to stirring the Yakisoba.

"Still, Nanako. The boy has to make his own decision and forge his own path in the world. If decides to become rogue, I-" His voice became strained. "I can't bear being responsible for creating yet another uncontrolled weapon of mass destruction on my conscience. It would be too-"

He never finished the sentence, and the tense air was left hanging.

Nanako glanced back and watched her mentor somberly. A shadow passed over her eyes as she listened to him.

Dr. Stench continued, his voice growing shaky. "If that time comes, I don't know if I can put...put down Genos. I owe the boy his entire future-"

Nanako ruthlessly interrupted. "When that time comes, if it comes" She turned her back to him, but Dr. Stench caught her icy stare. If anything, her tone was lethal. "You won't be the one to put him down."

The silence between them now became so thick, it felt almost palpable. Nanako was still engaged in her task, but he could tell her mind wasn't in it anymore. Dr. Stench shook his head, left his chair and laid a gentle hand on Nanako's shoulder. "I can't stain your hand with blood, Nanako. I can't turn you into a murderer." He said sternly, but there was a shade of softness in it. "I know you, child. You love all living creatures. You wouldn't be able to do it."

Nanako didn't reply to his words, which meant she was not yet dissuaded. But neither did she deny the truth in what he said. Nonetheless, the old scientist knew that Nanako's desire to protect him, who was perhaps the last of her family, could potentially spur her on to keeping that promise- no matter how much it was against her nature.

 _Youngters these days sure are hot-headed._ He chuckled wonderingly.

"Neither would you, Doctor. Not only do you feel indebted to him and pity him, can you really do that to someone you worked so hard to save?" Nanako asked, the sharp glint in her eyes already fading. Her face was now one of mild concern and worry.

Dr. Stench patted her head affectionately, smiling. "I don't know what will happen, Nanako, but we still have time on our sides. Genos' transformation is far from complete, even though he already wagered his limbs. As of now, he poses no threat. No doubt he can become strong in years to come, but we still have a couple of years on our hands to observe his character. Now, it is as you said. We can only do our best and have faith in the boy. I sense he has a good heart."

After a moment, Nanako caved in and said. "I'll trust your judgment, Doctor."

Dr. Stench chuckled. "Ha ha. Don't, my dear. I need someone to scrutinise my actions and right me when I'm wrong. Just be your vigilant self."

Nanako sighed and turned off the stove. She reached up the cupboard for some plates to serve their Yakisoba. "Yes, Doctor. Would you mind passing me the kettle?"

As she started to pour the hot water into a teapot, Dr. Stench began to set the table and laid down some porcelain cups. Their meal passed pleasantly, their conversation topics light and daily-focused. A good-humored atmosphere flowed easily between them and neither mentioned Genos' future again. It was until when Nanako had put away the dishes and was drying them on a rack that Dr. Stench was suddenly struck by an idea.

"By the way, Nanako, there is a favour I want from you." He told her, tone as blithe as if he were inquiring tomorrow's weather.

Curious, Nanako turned back and listened as the doctor explained just what his 'favour' entailed and required of her. When he finished, she jerked back in disbelief, face flushed.

"Doctor, you're not SERIOUS?" She exclaimed in dismay. "No! You'll never get me to do it."

"That's why I told you it was favour now, didn't I?" Dr. Stench grinned mischievously, looking as though he might have to suppress a giggle.

The truth was that Nanako had always found it impossible to ignore Dr. Stench's bidding. Like a granddaughter should heed her grandfather's words, she felt it was very much her duty to carry them out without any objection.

"I guess I can do it. But just so you know, Doctor - if he knocks his head and passes out or something, it's _not_ my fault."

Dr. Stench beamed, looking up from his paperwork and cup of tea. "You're a saint, Nanako."

.

.

.

* * *

A/N:

Finally, I was able to upload chapter 2. I thought it would be unreasonable to assume that Genos' transition from human to cyborg was overnight. Rather, it would be a gradual process that could take possibly years until he became the Genos we all know.

I also thought 15-year-old Genos is slightly different from 19-year-old Genos. While I'm probing the possibilities, I'll leave you guys to imagine how things turn out XD

Please review!


	3. Chapter 3: New steps

3

New steps

* * *

Genos was bored out of his mind. It had been a month since he was admitted in here. While it was out of his own volition that he be transformed into a cyborg, he had began to wonder lately if he had been here too long.

Dr. Stench had done done everything he could to provide Genos with comfort, bringing him books he might like to pass his time, introducing a vinyl record player for him to listen to music, and even asked Genos if he knits ('Only in my spare time, sir') but even those things eventually became dull and began to wear on his mind.

He often wondered how long had it been since he lasted looked upon the sky, the last time he saw the sun and stars. The thought suddenly seemed more appealing to him than anything. He was told he had made a remarkable recovery, and he felt he had enough strength in the current moment to go for short walk.

So he carefully flipped over the pure white sheets and inched himself to sat the edge of the bed. With that, he focussed all his attention into the effort of lifting himself up. The second he did, a wave of vertigo broke upon him and Genos felt ready to throw up. To his luck, he had eaten nothing since he woke up - his life-support tubes had been removed so as to allow him to rest in peace the night before, for which he had another reason to be particularly grateful.

It was a slow, painstaking process. He managed to make his way to the door, and not after falling over at least once. His body ached and begged him to return to the comfort of his bed, but he refused to relinquish. He started up again, gritting his teeth and this time somehow managing to get his balance.

He tried not to lean heavily on the door and put his weight on his good foot. With a fumbling hand he tried to twist the doorknob. After several failed attempts, the metal knob turned and the door stepped back to let him out.

Genos sighed in relief. It was his first step of freedom in weeks. He looked around, taking in the several doors nestling next to his. Each was marked with something different, so Genos was quick remember where his own room situated. So that he could return once his expedition was over.

Once he was in the hall, he repeated the same struggle and followed the wall closely, his spirit triumphing with every step forward and not backwards.

But Genos' luck would only last him half way across the hall.

"Hey Spongehead, you're not listening again."

Genos' brows twitched in slight annoyance as he turned to see Nanako. She was wearing a blouse which looked quite old and a skirt that flared around her ankles. On top of that, she was wearing the most patronising look he's seen in any kid. Maybe that glowingly gentle presence he remembered when they first met was just another side-effect of disorientation.

He'd seen here a few times since they first met, but very rarely. And more than half the time she was with Dr. Stench. He didn't pay much attention to her more than what was required. It wasn't as if she came to visit him anyway. They didn't speak to each other, since she usually left the talking to him and Dr. Stench. He was surprised that she sought him out today.

"Dr. Stench told you not to move around, didn't he? Why do you have to make it your mission to disobey everything he told you?" She asked, crossing her arms.

"I'm not disobeying anything the Doctor told me." Genos said, voice monotone. Of course he didn't. Dr. Stench never forbid him to leave, did he? He only instructed that Genos rested as much as possible and...

"Then why the hell are you in the hallway!?" She exclaimed impatiently, looking as though she'd charge at and arrest him at any moment.

Genos winced. He wasn't afraid of just _one_ girl (especially one who looked so light the wind would have blown her off). But with how delicately he had to move his body at the moment, he feared any more than necessary may cause his body to collapse.

"I need to start walking and build up my strength, or else I'm going to be lame the rest of my life." Genos explained. He wanted to quickly end this little squabble. It was getting pointless, and would benefit in nothing but to give him another headache. But his opponent clearly wasn't going to relent.

"Oh, _that_ sounds tempting." The girl, Nanako added sourly. "Too bad you won't."

"What?"

She smirked knowingly. "Get away with either. I'm taking you back to your room."

"No."

"A nurse doesn't need approval from his patients." She retorted.

In what nightmare? Genos thought to himself. He was growing suspicious. Does she even have nursing experience?

"Hey, you're thinking something rude, aren't you?" She accused him, lowering her voice dangerously. Genos knew he had to stand his ground.

"No," He said quickly. "I'm walking myself back."

"Hmm, _bad_ idea. You might damage that prosthetic leg of yours cause you're not used to it." The girl hummed. But at least she stopped.

 _Oh, it's the prosthetic leg you're worried about, obviously._ Genos thought to himself sarcastically. Girls are so difficult to deal with, most of all this girl in front of him right now.

"Well? Go on then." The girl urged.

Genos was taken back by her response. Was she going to let him do what he wants? He didn't she would. Okay, it wasn't as if he was going to let a flimsy girl like her carry him back anyway (he still had a bit of dignity to preserve). But for her to give in so easily when she protested so strongly two seconds ago...

"I never said I'd go back right away." He turned away, as if doing that would block out his troubles. Before she could protest, he added, "Don't worry. I intend to come back, **after** I've completed my objective and gone outside."

She grew quiet, her pretty features taking a serious turn. She looked caught up between wanting to shove him back to where she thought he belonged, and...something else. It was like she caught Genos cheating, but wanted badly to cheat herself. Unluckily though, she also wanted to turn him in.

She eyed him skeptically. "Do you even know the way out?"

Genos nodded calmly. "I can read. There's the exit sign."

She glanced briefly at the green board pointing the direction. "Oh, so you're interested in taking the stairs?"

She looked him up and down, clearly not impressed with his plan. Her eyes rested for a moment longer on his prosthetic right leg, where he was trying to put on as little weight as possible while gingerly balancing himself.

Genos decided he had enough time chatting with the girl. He should just focus ahead and get some damn fresh air already. At this rate, he'd arrive at somewhere in a couple of lifetimes.

The girl watched silently behind him. Without looking back he **knew** she was not very happy that he decided to be stubborn. After a while, it seemed as though she either left or was magnificently quiet. There was no other sound or noise other than the occasional tap of his prosthetic foot against the floor as he forced himself to walk. When he reached the end of the hallway, he was breathing heavily.

In his mind, Genos wondered if the girl gave up and went away already.

Curiosity got the better of him, and he stole a glance backwards.

Immediately, two things happened.

One, his fingers failed to give him purchase on the wall. He felt a yank of pain as his body collapsed. For a minute, he lost control of his body and was utterly paralysed. His eyes widened, his heart began to beat against his chest.

In that minute, it was as if he was under the rubbles again. Unable to move. Unable to lift a finger. Unable to even stand up or die. Helpless and at the mercy of God. God, who if he existed had abandoned him. Had not helped his family. His friends nor his hometown to survive.

He was dying again.

But then there was a soft hand. Its touch was light, but it steadied him easily. Suddenly, he was being held firmly in someone's arms.

"-p out of it, Spongehead. Don't waste yourself here."

Someone said it. Genos had the urge to be annoyed. ...He was sure he would be annoyed, if he wasn't feeling so out of it.

Whoever said it could not be this gentle.

"Genos."

That made him nearly gasp. That snatched him back a little, right as he was about to slip away. He was sure his life signs were growing cold. But the sound made something within him flare up. A tiny bit of warmth in his cold chest.

"Genos." The voice called him again. "Wake up."

Why was he responding to this voice? It was calling him.

Why was he responding? It wasn't even his name.

It took nearly all his current strength to muster a single word. "N-Nanako?"

"Yeah, I'm here." She replied.

He would told her he was drowning, but there was a lump in his throat. And he could not command himself to speak. It was so pathetic, that he couldn't even explain. But he sensed that he didn't need to. Nanako understood.

Genos found himself suddenly deeply exhausted. He suddenly wanted to sleep. Every inch of his body felt tired and defeated again.

A soothing hand patted his back, making comforting vibrations ripple through his body. Then, the hand moved to smooth out his hair from his face.

With that, Genos fell peacefully back to sleep.

* * *

 _To be continued..._


End file.
